Believer

From Command and Conquer Wiki

Believers were the lowest rank of the cultists led by Mortimer. They wore regular civilian clothing and looked over by the cult's priests. They were fanatics entirely devoted to the cult, who spent most of their time worshipping Tiberium and it's plant- and wildlife, attacking only when ordered to by the cult's priests. Interestingly, they were completely immune to Tiberium.

The lowest caste of the Bolivian Tiberium cult has disappeared after the demise of Mortimer.